1. Field of the Invention
The invention relates to a method for detecting eccentricity of an optical disc, and an optical disc drive configured by a computer program to perform the method.
2. Description of the Related Art
During a reproduction or recording operation of an optical disc drive, eccentricity of an optical disc may affect servo system control, which may disrupt the reproduction or recording operation. Hence, it is important to detect the eccentricity of the optical disc beforehand so that appropriate compensation may be conducted in order to ensure the integrity of the reproduction or recording operation.
In U.S. Patent Application Publication No. 2003/0099175, there is disclosed a process for computing eccentricity of a disk upon rotating. The process includes steps of starting a servo control system of a disk drive to rotate the disk at a specified angular velocity, measuring a track crossing speed of the servo control system at a focusing point on the disk (i.e., the optical disc drive is in a focused state but not in a track-locked state), and computing the eccentricity of the disc according to the specified angular velocity and the track crossing speed. In the proposed process, the track crossing speed is obtained from a tracking error signal. However, since the tracking error signal is also generated when a target optical disc is scratched, warped, or has a slightly offset center, miscalculation of the eccentricity of the disk is likely to occur.
Other methods for computing the eccentricity of an optical disc while an optical disc drive is in a focused state but not in a track-locked state are disclosed in U.S. Pat. Nos. 6,370,094 and 6,452,882. In the proposed methods of the aforesaid patents, disc eccentricity is determined as a function of the track pitch and the detected number of track crossings upon rotation of a disc. However, in the aforesaid patents, a normal optical disc having a high capacity and a low track pitch is easily misjudged as an eccentric one since a larger number of track crossings is detected within a same unit time period (or same displacement amount).